Technical Field
This disclosure generally relates to resistors, and more particularly, to active differential resistors that have reduced noise.
Description of Related Art
Resistors are fundamental and commonly used components in electronic circuits. Passive resistors generate what is known as Johnson-Nyquist or thermal noise. Such noise is generated by the thermal agitation of the charge carriers (e.g., electrons) inside a passive resistor regardless of whether a voltage is applied. Johnson-Nyquist noise is white in that its power spectral density is uniform throughout the frequency spectrum. It is governed by the relationship of Equation 1:VJohn/√{square root over (Hz)}=√{square root over (4kTR)}  [EQ. 1]
Where:                k is the Boltzmann's constant (joules per kelvin);        T is the resistor's absolute temperature (kelvin); and        R is the resistance of the resistor (Ω).        
The Johnson-Nyquist noise is generally considered to be a noise limit of a resistor and therefore an unavoidable source of error and/or undesired random disturbance for many applications that use a resistor. Reducing or overcoming the Johnson-Nyquist noise could dramatically change the application of resistors in various circuits.